Diving Into The Water: Cues Related to the Decision‐Making by an Egg Parasitoid Attacking Underwater Hosts

Abstract

Although adult parasitoids spend a majority of their lives above ground, females of several species must search for their host in the water or on the soil. Adult parasitoids above ground can use a variety of sensory cues to detect their hosts from a distance. However, their sensory cues can be impaired from volatile chemicals, and their visual stimuli can be decreased while submerging or burrowing in the water of soil during their search for their hosts. Searching underwater or underground would incur high foraging costs, that is, time and energy consumption and increase risk of drowning. Therefore, to reduce such costs and increase searching efficiency, the decision on where to start submerging or burrowing for attacking hosts is important for parasitoids. Furthermore, there are no studies that have examined the cues of submerging or burrowing parasitoids on their exploit for the decision to attack their hosts. We have examined the cues used by the egg parasitoid Tiphodytes gerriphagus attacking underwater hosts. We compared the searching behaviors of T. gerriphagus among four oviposition site conditions. The four sites investigated were oviposition site with both host adult chemical residues and presence of eggs, with only the presence of eggs, with only the host adult chemical residues, and without any cue. Our results indicated that T. gerriphagus more frequently contacted and submerged at oviposition sites with the adult residues rather than at oviposition sites without them. Nonetheless, the presence of underwater host eggs did not affect the host‐searching behavior. This suggests that T. gerriphagus decided to submerge at the oviposition site in response to the adult residues. Furthermore, our observation also suggested that T. gerriphagus has already detected that the adult residues might be volatile before contacting the oviposition site. Finally, we will discuss the exploitation patterns of host‐searching cue by parasitoids that need to submerge from the context of its reliability and detectability problems.

Presence of conspecifics triggers host searching behavior in an egg parasitoid wasp

“…There is a possibility that females used the presence of conspecifics as a cue about the existence of hosts ('social cue'; reviewed in Dall et al, 2005). Because female T. gerriphagus are attracted to chemicals left by ovipositing adult hosts (Kohmura et al, 2015), the presence of conspecifics may indicate the existence of host eggs. The number of unparasitized hosts probably decreases in a patch with conspecifics, but may not be zero.…”

“…), the underwater activity of T. gerriphagus seems to consist of searching for hosts. Chemical residues of adult water striders trigger host searching behavior, underwater host eggs do not affect their behavior (Kohmura et al, 2015). Females also sometimes submerge at substrates without such chemical traces or host eggs (H Hirayama, pers.…”